USB CDC Communications for Dummies!

[Squibcakes]

Want to communicate with your PIC via USB?
Want to install a virtual Commport on your PC?
Want to send serial commands to your PIC?

Its REALLY easy! Here's how.

Get yourself a PIC18F2455/2550/4455 chips that has USB support. And connect the Usb to to your PIC as shown below.

Note if using the USB bus power to power your pic remember that the max current your pic circuit can draw is 100ma! Anymore and you may blow your usb port! If in doubt stick in a fuse, or use external power.

For this demo though you can safely use the Bus Power. Mecanique has a good circuit diagram you can follow here. http://www.mecanique.co.uk/products/...atic-large.gif

Pin Name Cable color Description
1 VCC Red +5 VDC (Vdd)
2 D- White Data - (RC4)
3 D+ Green Data + (RC5)
4 GND Black Ground (Vss)

Once your hardware is setup follow on....

STEP ONE.

In your PBP folder, copy the entire contents of the USB18 folder into a new folder where you store your pic programs;

eg... copy c:\pbp\usb18\*.* c:\cdcdemo

STEP TWO.

Open the USB descriptors file (called USBDESC.asm)
There are three lines of code in there, change the ; so that CDCDESC.ASM is used.

;	include "MOUSDESC.ASM"		; USB descriptors for mouse demo
;	include "JADESC.ASM"		; USB descriptors for Jan Axelson's demo
	include "CDCDESC.ASM"		; USB descriptors for CDC demo

STEP THREE.

Copy this code and save it into the c:\cdcdemo folder and then compile using pbp.

DEFINE    OSC 48

Buffer    VAR BYTE[16]
Cnt       VAR BYTE
B0        VAR BYTE
B1        VAR BYTE

ADCON1 = 15               ' Set all I/Os to Digital      
CMCON = 7                 ' Disable Comparators
Cnt = 16

USBInit                   ' Initialize USART

for b0 = 0 to 15
    lookup b0,["USB CONNECTED!",10,13],B1 
    BUFFER(B0) = B1
    NEXT B0

' Main Program Loop
Loop:
    USBService        ' Must service USB regularly
    USBOut 3, Buffer, Cnt, loop
    goto loop
end

When you compile the above program, PBP fuses the USB18 files in youe cdcdemo folder to generate the neccessary .HEX file. Viola!!
run your progam.

Windows will detect the PIC as a USB device and install the Microchip CDC driver.

STEP FOUR.

Open up Hyperteminal and select the virtual comport that was just installed. you should see USB CONNECTED! repeated.

Congratulations, you can send data from the PIC to the PC via a quasi Serial connection.

Ok How about sending and receiving data?

Program this code below into your pic:

buffer	Var	Byte[16]
cnt	Var	Byte
LED	Var	PORTB.0

Define  OSC     48

	USBInit
	Low LED		' LED off

' Wait for USB input
idleloop:
	USBService	' Must service USB regularly
	cnt = 1	' Specify input buffer size
	USBIn 3, buffer, cnt, idleloop

' Message received
	Toggle LED

outloop:
	USBService	' Must service USB regularly
	USBOut 3, buffer, cnt, outloop

	Goto idleloop	' Wait for next buffer

Again open Hyperterminal and the PIC will echo back the characters that you type (one byte at a time).

Try sending a large text file. Does it keep up?

Wow your becoming an expert now aren't you!

Stay Tuned....
Squib

[Bruce]

Nice work Squib...;o}

[T.Jackson]

Nicely done. Worth a vote...

It would be great to see a lot more practical examples posted. Even better if there's an electrical schematic included as well.

Best Regards,
Trent Jackson

[mister_e]

[Pic_User]

Beautiful, step by step “how to” piece of art. Thank you Squib. Nicely done.
-Adam-

[vacpress]

thanks squib!

you are great.

[ricgar]

Hi Squipcakes

I've followed your instructions for this post and built the schematics attached which are very similar to yours posted (see attached). But once compiled and loaded onto the chip, the chip's power led lights up but the diagnostic led's don't and the PC doesn't even see a device attached to the system. I've checked my connections and they all seem fine. I have also attached the files used to make the hex and the hex (file is the mycdc.hex). I'm using a PIC18f2450 (not the same as in the schematics but same pinning)

What could be the problem??

Thanks

[kirtcathey]

Hi All. Thanks in advance for the help.

I am in a similar situation as the respondent above. Have setup everything with an 18F2550 and when plugged in, device not recognized error appears in XP. Where are the CDC drivers mentioned? A lot of the posts above applaud the project, but when a real implementation question is asked, it gets quiet.

Please, throw the dog a bone!

Regards,
Kirt

[kirtcathey]

Okay, I have got my problems down to matching VID and PID numbers in the mchpcdc.inf file and the VID and PID numbers burned on the PIC (18F2550).

Have looked in cdcdesc.asm, but don't know where to find these values.

Any help?

[kirtcathey]

Well.... I figured out the PID and VID stuff... The values in the cdcdesc.asm file and the values in the inf file of the driver (CDC this time) you are using must match.

After confirming this, XP still recognizes that a USB device is attached, but when I go to install the CDC driver, an XP dialog that says hardware information cannot be found appears.

Any help?

[arniepj]

Its been awhile since I went through the same project, but I don't think you need to modify those files.The pic config settings needs to be correct though.I have attached a project folder with files I did once I had it working.Look through the the files for possible clues,primarily the .bas for the config settings.
It uses a 4mhz crystal.
Good luck

[sputnik77]

arniepj, I cannot get your code working either.

There are no config fuses set in the code, and I do not know what they are supposed to be for this application.

I cannot fing any hints in your code as to how to get it to work.

Any help is much appreciated.

[OzGrant]

G'Day,
Used Mecanique cct(20M 18F4550) and PBP2.6 and after adding

@ __CONFIG _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@ __CONFIG _CONFIG1H, _FOSC_HSPLL_HS_1H
and then enabling VREGEN config bit got the Windows USB Device Not recogised message.
Are there any other config bits that have to be changed.
Is it possible to get a hex file for this project so I can at lest check my cct.
tks

[OzGrant]

G'day (again)
My problem cured when I added a 10MFD cap on the two 18F4550 power pins.
I was using the USB 5v to power the card.
So can now start playing(at last) with USB.
Grant

[f_lez]

Windows sees a pic18 usb cdc device s inserted, but finds no drivers.

windows 7 32 bit

[f_lez]

yes the above error was me stupidly not showing windows device mangler where the right .inf file was, my bad...

But..

I am now doing a ' USBIN endpoint, buffer, count, nodatatloop ' every second or so, problem is when I send data to it, I only get it one byte at a time, so reading 'cat' takes 3 seconds......

count variable is always 1 if data present, so i get 1 three times then it returns to zero

surely I should get all 3 bytes into my buffer and a value returned of 3 for count.

I dont lose any chars from my text string in the terminal, i think it buffers and does some form of flow control, but when i copy a text file in a dos/command window, i do lose them, i get a count of one for the first 'C' but then a zero as 'at' have got lost before i got a chance to read them.

[f_lez]

Ok cant edit the above but it goes like this, if i send 'cat' with hyperterminal or putty i get 3 individual chars at the pic end so need to read 3 times, if i send it from a program written in vb6, i get a 'cat' in one loop/poll etc and a bytecount length of 3, as expected, hope no one else falls foul of this.